Luke and I each have a wiggy's bag (I forget which models, but they each are a bag with an optional overbag--I think mine is rated to -30 and Luke's to 0).
For summer or early fall trips where we don't expect super cold/wet weather, we use our down bags or quilts instead, but there are some circumstances in which the Wiggy's are well worth their weight and bulk. Synthetic fill means they provide warmth even if they get wet, making them a good choice for very wet conditions (think Kodiak island in October or November). Because they are the warmest rated bags we own, they also get the nod for winter camping trips. Most often use them when we can haul them with snowmachines (mobiles for you lower 48 folks) or ATVs, but we have backpacked with them a couple of times when we felt the extra insurance was worth the weight. We got one bag with left zip and one with right so that we can zip them together into a double bag when we want to.
As someone else mentioned, they are well made with super stout zippers. I have never been cold in mine yet. Leaving tomorrow for 5 nights winter camping/ice fishing/ptarmigan hunting and my wiggy's bag was the obvious choice....
